hacking up my yak

[dsafety]

Originally Posted by bubblehide

Someone had mentioned that I may have the fastest yak out there once done; I'm honestly not sure about this. I would say I would end up with a more efficient kayak. I guess what I'm saying is that it should be faster off the line, i.e., more efficient. But when it comes to top speed, I think it's a combination of hull design and the pedal drive units abilities; and I feel that the design of the drive unit has it upper speed output limits. So I don't expect to gain any significant speed over another pedal drive yak, given consideration for hull design/speed ability. But I do expect the yak to do what ever speed with more efficiency It's that efficiency that makes the Hobie's so damn appealing and well worth the extra dough.

I am not a naval engineer or anything close but if I remember correctly there is something called "hull speed" that determines the maximum speed that a single hull vessel can reach without coming to a plane. It has something to do with displacement, drag and probably some other factors. At some some speed, the hull starts to create bow waves which offset increases in thrust. Simply put, when a vessel reaches its hull speed, increases in thrust are counteracted by increases in resistance so the thing will not go faster regardless of how much propulsion is added.

Apparently there are exceptions to this rule. Racing kayaks are an exception. These boats can go reach speeds that are nearly twice their theoretical hull speed. I have no idea why.

My guess is that since your hull is a faster design to begin with you will have a higher hull speed than the Hobies. I also think that there is a good chance that the increased efficiency of the hull will make it so you will get more thrust with the same energy. This should help improve your maximum speed as well.

Time will tell. Regardless of how everything turns out, it looks to be a fun project.

Bob

[805gregg]

[QUOTE=dsafety;76126]I am not a naval engineer or anything close but if I remember correctly there is something called "hull speed" that determines the maximum speed that a single hull vessel can reach without coming to a plane. It has something to do with displacement, drag and probably some other factors.

It's waterline length, there is a mathamatical formula, and unless you can plane, you are limited to that speed. It's something about wave formation or something. I do know on my 28' displacement sailboat it's about 6.2 knots, I could put 400 hp and not go faster, it will go 6.2 knots with the 15 hp diesel, I have. And use 1 qt per hr.

[-scallywag-]

Cool idea!!!


It doesn't surprise me that a former outback owner would feel this way, specially if you owned a 1st gen hull (with the round front hatch). And didn't you return your hobie because it didn't steer itself? I think Hobies "ill handling hulls" are actually designed that way. You have to consider that the large majority of people out there are using them in calm waters, and really enjoy the quick boat-like response of the Hobie hulls. Not to mention, who actually paddles these things? Remember the Outback is still, by far, the best seller.Having a hull that tracks well will not feel as playful in the water, and would also scrub off a lot of speed every time you do turn.


Enter the Adventure....long and sleek (27.5"W vs. 31"W) and as close to a true SIS touring style hull as I've seen on any SOT (besides maybe the 160i, prowler and expedition)....granted the area under the cock-pit is a little flatter, giving up some tracking but not much. I can't imagine someone into speed and efficiency "hating" this hull design.....although I do imagine that there are plenty of people out there who are a little afraid of trying to fish from a 27.5" wide platform. Maintaining speed/efficiency, especially in rough water has a cost, and generally it is stability.


As for the surf...well, IMHO it has a lot more to do with the skill and strength of the paddler along with the weight distribution in the kayak. Hull design and width, not so much!!

Anyway, I can't wait to read the rest of the build along with the testing and tuning afterwards. Hopefully you can hook-up with a local Hobie guy "roadrunner" and do some performance testing. In the past he has put most of the Hobie hulls though some pretty extensive tests.

FYI, the "calculated hull speed" debate has already been beat to death...the equation is antiquated and has little use when discussing kayak hulls.

[bubblehide]

Originally Posted by -scallywag-

Cool idea!!!


It doesn't surprise me that a former outback owner would feel this way, specially if you owned a 1st gen hull (with the round front hatch). And didn't you return your hobie because it didn't steer itself?

...

Nope, it wasn't a 1st gen, and no, I didn't return it.

[dsafety]

Originally Posted by -scallywag-

FYI, the "calculated hull speed" debate has already been beat to death...the equation is antiquated and has little use when discussing kayak hulls.

Scally, for those of us not in the know, please explain the above statement.

Bob